The long-term goal of this project is to understand the mechanisms for cannabinoids to lower intraocular pressure (IOP), and to provide a basis for developing novel cannabinoids with improved IOP-lowering properties, and devoid of psychoactive side-effects of marijuana. The central hypothesis to be tested in this proposal is that cannabinoids act on specific cannabinoid receptors in multiple targets of the outflow pathways to exert their IOP-lowering effects. To test this hypothesis, the following specific aims are planned. (1) To test the effects of cannabinoid ligands and the roles of cannabinoid receptors on outflow facility with perfused human ocular anterior segment, using recently developed high affinity and/or subtype-selective cannabinoid ligands. (2) To map the distribution of cannabinoid receptor subtypes in two potential targets of cannabinoids, trabecular meshwork and ciliary muscle. (3) To characterize ligand binding properties and signal transduction mechanisms of cannabinoid receptors in trabecular meshwork and ciliary muscle cells. (4) To determine the effects of cannabinoid ligands, the roles of cannabinoid receptors, and cannabinoid signaling pathways in regulating the cellular functions (such as cell cytoskeleton and matrix metalloproteases) of trabecular meshwork and ciliary muscle cells. A combination of molecular biology, cell biology and pharmacology approaches will be applied to the proposed research. Attempts will be made to correlate information gained from in vitro experiments with ex vivo organ perfusion studies in order to understand the roles of cannabinoid receptors and the mechanisms for the effects of cannabinoids on aqueous humor outflow. By investigating the mechanisms underlying the IOP-lowering effects of cannabinoids, this study may facilitate the discovery of more effective anti-glaucoma cannabinoid ligands. By deciphering specific ocular cannabinoid receptor subtypes that are involved in the IOP-lowering effects of cannabinoids, this study may help to separate the desired IOP-lowering effects of cannabinoids from their undesired psychoactive side-effects.